1. Field of the Invention
The present invention relates to an abnormal state detecting apparatus in a torque sensor which uses a pair of coils to detect a torque on the basis of a change in inductance.
2. Description of the Related Art
In a torque sensor with a pair of coils whose inductance mutually reverses direction in accordance with a torque, a differential amplifier circuit which differentially amplifies a pair of detection voltages induced to the pair of coils when receiving the detection voltages. A torque is then detected from the output of the differential amplifier circuit. In order to diagnose an output of the differential amplifier circuit, the same circuit is connected to the pair of coils in the same manner so as to detect a difference between the outputs of both the differential amplifier circuits.
A pair of rectifier circuits are respectively connected to both of the coils, and respective outputs of the pair of rectifier circuits are respectively input to the differential amplifier circuit via buffer circuits. A circuit constituted by the same pair of rectifier circuits, buffer circuits and differential amplifier circuits is connected to the coil in parallel.
When any of the two pairs of four rectifier circuits are out of order, a difference is generated between the outputs of both of the differential amplifier circuits and an abnormal state can be detected. In the case that only one pair of two rectifier circuits are provided, the outputs of both of the differential amplifier circuits have the same value even when one of the rectifier circuits is out of order. Therefore, no difference is generated therebetween and an abnormal state can not be detected.
Accordingly, there are two pairs of four circuits constituted by the same rectifier circuit. The high number of, circuit constituting members creates a complex circuit.
The present invention is made by taking the points mentioned above into consideration. An object of the present invention is to provide an abnormal state detecting apparatus of a torque sensor which can simplify a circuit by reducing the number of rectifier circuits.
In order to achieve the object mentioned above, in accordance with the present invention, there is an abnormal state detecting apparatus of a torque sensor. This is comprised of a pair of coils whose inductance mutually reverses in accordance with a torque, and a pair of rectifier circuits respectively connected to the pair of coils. A first differential amplifier means inputs the respective outputs of the pair of rectifier circuits as first and second sub-voltages via buffer circuits, and amplifies a difference between the first and second sub-voltages and outputs the difference as a first main voltage. A second differential amplifier means inputs branch outputs obtained by branching the respective outputs of the pair of rectifier circuits as third and fourth sub-voltages via buffer circuits, and amplifies a difference between the third and fourth sub-voltages and outputs the difference as a second main voltage. There is a control means which detects a torque on the basis of the first main voltage corresponding to the output of the first differential amplifier means and diagnoses the first main voltage by means of the second main voltage. A memory means stores a corresponding relation between any one sub-voltage selected among the first and third sub-voltages previously calculated in a normal state and any one sub-voltage selected among the second and fourth sub-voltages. An abnormal state judging means inputs a pair of sub-voltage values corresponding to the selected pair of sub-voltages and compares the input pair of sub-voltage values with the corresponding relation of the pair of sub-voltages stored by the memory means so as to judge whether or not an abnormal state exists.